Rotary joint

ABSTRACT

In a rotary joint A including an electric signal slip ring  31  for passing different electric signals between a stator  1  and a rotor  6 , for the purpose of stable transmission of electric signals in the electric signal slip ring  31 , stationary side electrode stacks  38   a  and  38   b  are provided individually by stacking each pair of axially adjacent two  36   b  to  36   e  of six ring-plate-shaped stationary side electrodes  36   a  to  36   f  arranged concentrically with the axis of the stator  1  and aligned axially with each other together with one of stationary side insulating seats  37   a  and  37   b  interposed between the pair of axially faced stationary side electrodes, rotating side electrode stacks  42   a  to  42   c  are provided individually by stacking each pair of axially adjacent two  40   a  to  40   f  of six ring-plate-shaped rotating side electrodes  40   a  to  40   f  arranged concentrically with the axis of the rotor  6  and aligned axially with each other together with one of rotating side insulating seats  41   a  and  41   c  interposed between the pair of axially faced rotating side electrodes, a group of the stationary side electrode stacks  38   a  and  38   b  and another group of the rotating side electrode stacks  42   a  to  42   c  are arranged between the axially distally situated stationary side electrodes  36   a  and  36   f  so that one from one group and one from the other axially alternate and all in each group are axially aligned, and a plurality of spherical bodies  44  are disposed between each of the distally situated stationary side electrodes  36   a  and  36   f  and the electrode of the rotating side electrode stack  42   a  or  42   c  axially faced to each said distally situated stationary side electrode  36   a  or  36   f  and between the faced electrodes of the axially adjacent stationary and rotating side electrode stacks to roll on the faced electrodes to pass electric signals between them.

TECHNICAL FIELD

This invention relates to a rotary joint disposed, for example, at thedistal end of a robot arm, and particularly relates to a technical fieldregarding measures for stably passing electric signals between a statorand a rotor.

BACKGROUND ART

Conventional rotary joints of this kind have a stator fixedly mountedto, for example, the distal end of a robot arm, and a rotor fixedlymounted to a hand side of the robot and rotatably coupled and supportedto the stator, and are configured to allow communication of fluid, suchas air, cooling water or welding gas, and electricity for power, signalsor other purposes between the stator and rotor so that communication ofsuch fluid and electricity can be established even when the hand side ofthe robot rotates with respect to the stationary side thereof.

Furthermore, for fluid communication, the above rotary joints employ aswivel joint in which plural kinds of fluid passages are arrangedbetween the slide surfaces of the stator and rotor. For powerelectricity communication, the above rotary joints employ a slip ringconsisting of a collector ring mounted to one of the stator and rotorand a slide contact mounted to the other for coming into sliding contactwith the collector ring to feed electricity.

There are also known electric signal slip rings for passing electricsignals between a stator and a rotor. Proposed as an example of suchelectric signal slip rings is, as disclosed in Japanese UnexaminedPatent Publication No. 10-223346, an electric signal slip ring whichincludes a stationary side electrode of ring plate shape disposed on thestator side, a rotating side electrode of ring plate shape disposed onthe rotor side, and a rolling element disposed between both theelectrodes, and which is configured to roll the rolling element on boththe electrodes by relative rotation of the rotor to the stator to passelectric signals between both the electrodes.

The proposed electric signal slip ring, however, has a problem that whena plurality of stationary side electrodes and a plurality of rotatingside electrodes are arranged to pass different electric signals betweenthe stator and rotor, some or other of the electrodes may producesliding friction to make it difficult to stably transmit electricsignals between the stator and rotor.

Furthermore, electric signal transmission through rolling of the rollingelement on the electrodes, though making the occurrence of a slip of therolling element difficult, cannot avoid the production of wearparticles. When the wear particles accumulate on the conductive surfacesafter long-time use, it again becomes difficult to stably transmitelectric signals.

In addition, in order to ensure stable transmission of electric signalsthrough rolling of the rolling element, it is desirable to reduce thesliding resistance of the rolling element as much as possible.

The present invention has been made in view of the foregoing points, andtherefore its object is to improve the structure of the electric signalslip ring in the rotary joint as described above, thereby enabling, evenin passing different electric signals between the stator and rotor,stable transmission of the electric signals.

DISCLOSURE OF INVENTION

To attain the above object, the present invention, as described above,is directed to a rotary joint including a stator, a rotor rotatablycoupled and supported to the stator, and an electric signal slip ringfor passing different electric signals between the stator and the rotor,wherein the electric signal slip ring includes a plurality of stationaryside electrodes of ring plate shape arranged concentrically with theaxis of the stator and aligned axially with each other, and a pluralityof rotating side electrodes of ring plate shape arranged concentricallywith the axis of the rotor and aligned axially with each other.

Furthermore, a stationary side electrode stack is provided by stackingeach pair of axially adjacent two of the plurality of stationary sideelectrodes with a ring-shaped stationary side insulating layerinterposed between the pair of two stationary side electrodes, and arotating side electrode stack is provided by stacking each pair ofaxially adjacent two of the plurality of rotating side electrodes with aring-shaped rotating side insulating layer interposed between the pairof two rotating side electrodes. In addition, the stationary sideelectrode stack and the rotating side electrode stack are axiallyalternately arranged between a pair of end electrodes located at bothaxial ends of the electric signal slip ring, and a plurality of rollingelements are disposed between each of the end electrodes and theelectrode of the electrode stack axially faced to each said endelectrode and between the axially faced electrodes of the axiallyadjacent electrode stacks to roll on said two electrodes throughrelative rotation of the rotor to the stator to pass electric signalsbetween said two electrodes.

With this structure, a stationary side electrode stack is formed of onepair of the stationary side electrodes of the plurality thereof and thestationary side insulating layer, a rotating side electrode stack isformed of one pair of the rotating side electrodes of the pluralitythereof and the rotating side insulating layer, these electrode stacksare axially alternately arranged between one pair of end electrodeslocated at both axial ends of the electric signal slip ring, and theplurality of rolling elements are disposed between each of the endelectrodes and the electrode of the corresponding electrode stack andbetween the axially faced said electrodes of the axially adjacent saidelectrode stacks. Thus, while the rotary joint has a structure in whichdifferent electric signals are passed between the stator and the rotor,the rolling elements lie between each of the stationary side electrodesand the corresponding rotating side electrode for transmitting orreceiving signals from or to each said stationary side electrode, andthe stationary and rotating side electrodes relatively move whilerolling the plurality of rolling elements. Therefore, the occurrence ofslip on the electrodes is suppressed as much as possible, therebyproviding stable transmission and reception of an electric signalbetween each of the stationary side electrodes and the correspondingrotating side electrode.

In the above rotary joint, pressing means for pressing at least one ofthe end electrodes towards the other end electrode may be provided. Inthis way, the occurrence of slip between each of the stationary sideelectrodes and the corresponding rotating side electrode can besuppressed with higher certainty, thereby providing more stabletransmission and reception of an electric signal between both theelectrodes.

In a rotary joint including a stator, a rotor rotatably coupled andsupported to the stator, and an electric signal slip ring for passingelectric signals between the stator and the rotor, an air blowingpassage may be provided which has one end opening into the stator, theother end opening into the rotor and an intermediate part passingthrough the electric signal slip ring, and the rotary joint may beconfigured so that an air blowing operation of blowing air into the airblowing passage through one of an air blowing hole on the stator sideand an air blowing hole on the rotor side while relatively rotating thestator and the rotor and discharging the air through the other airblowing hole and another air blowing operation of blowing air into theair blowing passage through the other air blowing hole while relativelyrotating the stator and the rotor and discharging through said one airblowing hole is alternately carried out.

Alternately, in the rotary joint having the above inventive structure,an air blowing passage may be provided which has one end opening intothe stator, the other end opening into the rotor and an intermediatepart passing through the electric signal slip ring.

With these structures, even if wear particles are produced on theelectric signal slip ring because of wear of the electrodes and so on,alternate air blows into the air blowing passage through each of itsends allow the air flow to blow off the wear particles through the otherend of the air blowing passage together with the blown air. Therefore,wear particles can be removed with ease, thereby providing stabletransmission of electric signals between the electrodes for a longperiod of time.

It is desirable that the air blowing passage should include an electricwire insertion hole for inserting therein an electric wire connecting tothe electric signal slip ring. In this way, air can be blown on theelectric signal slip ring using the existing electric wire insertionhole, and therefore the structure of the air blowing passage can besimplified.

In the rotary joint having the above inventive structure, the electricsignal slip ring may include an outer housing fitted to one of thestator and the rotor, and an inner housing fitted to the other of thestator and the rotor and disposed substantially concentrically in theouter housing with an annular space created between the inner and outerhousings, and the stationary and rotating side electrodes may beaccommodated in the annular space between both the housings.Furthermore, one of the group of stationary side electrodes and thegroup of rotating side electrodes may be fitted and borne against theinner periphery of the outer housing with a certain clearance leftbetween the inner peripheries of said one group of electrodes and theouter periphery of the inner housing, while the other of the group ofstationary side electrodes or the group of rotating side electrodes maybe fitted and borne against the outer periphery of the inner housingwith a certain clearance left between the outer peripheries of saidother group of electrodes and the inner periphery of the outer housing.

With this structure, even if the axes of the stator and rotor, i.e., theaxes of the outer and inner housings of the electric signal slip ring,are misaligned relative to each other, the clearance between the innerperipheries of the electrodes fitted on the inner periphery of the outerhousing and the outer periphery of the inner housing or the clearancebetween the outer peripheries of the electrodes fitted on the outerperiphery of the inner housing and the inner periphery of the outerhousing is only eliminated, which stably rolls the plurality of rollingelements between the electrodes. Therefore, even if a misalignmentbetween the axes of the stator and the rotor occurs, it can be ensuredthat an electric signal is stably transmitted between the stationary androtating side electrodes.

In this case, raceways for rolling elements of the stationary androtating side electrodes may be formed in flat surfaces. Thus, theplurality of rolling elements can be rolled with higher stabilitybetween the electrodes. Therefore, even if a misalignment between theaxes of the stator and the rotor occurs, it can be ensured that anelectric signal is transmitted with higher stability.

The rolling elements and the electrodes in the electric signal slip ringmay each have a plated surface. In this way, the contact resistancebetween each rolling element and the adjacent electrodes can beconstantly held at a small value.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view of a rotary joint according to anembodiment of the present invention.

FIG. 2 is a cross-sectional view showing one side of an electric signalslip ring in enlarged manner.

FIG. 3 is a cross-sectional view showing the other side of the electricsignal slip ring in enlarged manner.

FIG. 4 is an enlarged perspective view showing the electric signal slipring with portions broken away.

FIG. 5 is a partly-broken, perspective view showing portions of a bossof a stator which form water passages and an air passage, respectively.

FIG. 6 is a perspective view showing the structure of a stationaryelectrode stack.

FIG. 7 is a perspective view showing the structure of a rotatingelectrode stack.

FIGS. 8A, 8B, and 8C are illustrations showing that the axes of housingsof the electric signal slip ring are misaligned.

FIG. 9 is a cross-sectional view showing air flows when air is blowninto the electric signal slip ring.

FIG. 10 is a plan view showing air flows when air is blown into theelectric signal slip ring.

FIG. 11 is a top view of the rotary joint.

FIG. 12 is a front view of the rotary joint.

FIG. 13 is a bottom view of the rotary joint.

BEST MODE FOR CARRYING OUT THE INVENTION

A best mode for carrying out the present invention will be described asan embodiment with reference to the drawings.

FIGS. 11 to 13 show a rotary joint A according to an embodiment of thepresent invention. This rotary joint A is arranged so as to be fitted tothe distal end of an arm of an unshown welding robot for carrying outspot welding.

The rotary joint A includes a stator 1 of substantially cylindricalshape mounted to an arm side of the welding robot, and a rotor 6 ofsubstantially cylindrical shape mounted to a welding gun side (a handside) thereof. The rotor 6 is coupled and supported for rotation with360 degrees or more to the stator 1.

As shown in enlarged manner in FIG. 1, the stator 1 has a cylindricalboss 3 formed integrally with an outward flange 2 at the top end (theupper end in FIG. 1), and a bottomed, cylindrical cover 4 that isdisposed concentrically to surround the boss 3, is secured integrally tothe boss 3 and downwardly opens.

The rotor 6 includes a cylindrical shaft 7 fitted relatively rotatablyinto the boss 3 of the stator 1, an upper flange 8 secured integrally onthe upper end of the shaft 7 to close the opening of the cylindricalshaft 7 and located in a portion of the rotor 6 above the outward flange2, and a lower flange 9 secured integrally about the lower end of theshaft 7 and extending radially outwardly beyond the bottom end of theboss 3 to close the lower opening of the cover 4.

Between the boss 3 of the stator 1 and the shaft 7 of the rotor 6, aswivel joint 11 is provided for communicating water and air as fluidsbetween the stator 1 and the rotor 6. Furthermore, in a cylindricalspace surrounded by the boss 3 and cover 4 of the stator 1 and the lowerflange 9 of the rotor 6, a power slip ring 21 for supplying weldingpower from the stator 1 to the rotor 6, and an electric signal slip ring31 located internally of the power slip ring 21 for passing differentelectric signals of plural kinds (six kinds in the example shown in thefigures) between the stator 1 and the rotor 6 are fitted concentrically.

The swivel joint 11 has two water passages 12, 13 and one air passage14, and these three passages 12 to 14 have the same structure.Specifically, as also shown in FIG. 5, the internal periphery of theboss 3 of the stator 1 is formed with three annular grooves 15, 15, . .. vertically (axially) spaced from each other. Furthermore, inside ofthe wall of the boss 3, three vertical holes 16, 16, . . . (only part ofthem shown) extending vertically are formed through the wall andcircumferentially close to each other. The lower end of each verticalhole 16 opens into the bottom surface of the corresponding annulargroove 15, while its upper end opens into the outer periphery of theoutward flange 2.

On the other hand, inside of the wall of the shaft 7 of the rotor 6,three vertical holes 17, 17, . . . (only part of them shown) extendingvertically are formed through the wall at circumferentially equallyspaced positions. The upper end of each vertical hole 17 opens into theouter periphery of the shaft 7 to communicate with the correspondingannular groove 15 in the boss 3 of the stator 1, while the lower end ofeach vertical hole 17 opens into the outer periphery of the shaft 7below the lower flange 9. The passages including upper two of the threeannular grooves 15, 15, . . . formed in the inner periphery of the boss3 of the stator 1 constitute the water passages 12 and 13, respectively,and the passage including the lower one 15 constitutes the air passage14. Through these water passages 12 and 13 and air passage 14, water andair can be communicated even between the stator 1 and the rotor 6 bothrelatively rotated.

Furthermore, the inner periphery of the boss 3 of the stator 1 is formedwith four sealing grooves 18, 18, . . . one on each vertical (axial)side of the three annular grooves 15, 15, . . . , and each sealinggroove 18 is fitted with a rubber-made sealing ring 19 so that the innerperiphery of the sealing ring 19 makes sliding contact with the outerperiphery of the shaft 7 of the rotor 6 to form a seal therewith.

Furthermore, as shown in FIG. 5, the opening of each vertical hole 16 inthe bottom surface of the annular groove 15 in the boss 3 of the stator1 is formed by perforating through the wall of the boss from the pointon the outer periphery of the boss diametrically opposed to a portion tobe opened of the bottom surface of the annular groove 15 and then makingthe opening in the bottom surface of the annular groove 15. Theperforation of the wall is closed in air-tight manner by a plug 20 afterthe making of the opening.

The power slip ring 21 is provided with three collector rings 22, 22, .. . concentrically arranged in the cylindrical space formed among theboss 3 and the cover 4 of the stator 1 and the lower flange 9 of therotor 6. The collector rings 22, 22, . . . are vertically stackedthrough individual insulating rings 23, 23, . . . . Each collector ring22 is screwed on the distal end (upper end) of a collector bolt 24 thatpasses through the other collector rings 22 in electrically insulatedmanner. Each collector bolt 24 passes through the lower flange 9 of therotor 6 in electrically insulated manner. Its head 24 a at the lower endprotrudes below the lower flange 9, and is connected with an end of apower cable 25 that conducts electricity to the welding gun (not shown).

Three slide contacts 26, 26, . . . pass through the sidewall of thecover 4 of the stator 1 at circumferentially equally spaced and mutuallyneighbouring positions in electrically insulated manner, and are securedto the sidewall of the cover 4 with each covered with a cover 26 a. Theinner end of each slide contact 26 is pushed slidably against the outerperiphery of the corresponding collector ring 22 with a predeterminedpressing force. The sliding contact between each slide contact 26 andthe corresponding collector ring 22 allows welding power at a largecurrent to be transmitted even between the stator 1 and the rotor 6 bothrelatively rotated.

Furthermore, the electric signal slip ring 31 is provided with acylindrical inner housing 32 fitted onto the outer periphery of the boss3 of the stator 1, and a cylindrical outer housing 33 fittedconcentrically onto the inner housing 32 with an annular space 34created therebetween as described later. Both the housings 32 and 33 aremade of resin, for example. The outer periphery of the inner housing 32is formed at the upper and lower ends integrally with outward flanges 32a and 32 b, respectively. The annular space 34 of cylindrical shape isdefined so as to be surrounded by both the flanges 32 a and 32 b, avertical intermediate portion of the outer periphery of the innerhousing 32, and the outer housing 33.

The annular space 34 between the inner and outer housing 32 and 33accommodates six ring-plate-shaped stationary side electrodes 36 a to 36f and six ring-plate-shaped rotating side electrodes 40 a to 40 f. Eachof these electrodes 36 a to 36 f and 40 a to 40 f is made of phosphorbronze, for example, and its surface is plated with silver, for example.Preferably used as a plating material for this plating is any goodconductive material having the effect of rust prevention of theelectrodes 36 a to 36 f and 40 a to 40 f themselves. The thickness ofthe plated layer is preferably small. The plated layer with a thicknessof 5 μm or less would be more preferable because it is less likely to bepeeled off. The top and bottom surfaces of each of the electrodes 36 ato 36 f and 40 a to 40 f, specifically, their raceways on which thelater-described spherical bodies 44 roll, are formed in flat surfaces.

As shown in detail and enlarged manner in FIGS. 2 and 3, the sixstationary side electrodes 36 a to 36 f are arranged concentrically withthe axis of the stator 1 and aligned axially or vertically with eachother, while the six rotating side electrodes 40 a to 40 f are likewisearranged concentrically with the axis of the rotor 6 and aligned axiallyor vertically with each other.

Among the six stationary side electrodes 36 a to 36 f, two electrodes 36a and 36 f located at the upper and lower ends (axial ends) are endelectrodes. For the four stationary side electrodes 36 b to 36 eexclusive of the two stationary side electrodes 36 a and 36 f as endelectrodes, as also shown in FIG. 6, the one pair of axially adjacentstationary side electrodes 36 b and 36 c are stacked with a ring-shapedstationary side insulating seat 37 a interposed therebetween, and theother pair of axially adjacent stationary side electrodes 36 d and 36 eare stacked with a ring-shaped stationary side insulating seat 37 binterposed therebetween. The one pair of electrodes 36 b and 36 c andthe other pair of electrodes 36 d and 36 e form two individualstationary side electrode stacks 38 a and 38 b with the stationary sideinsulating seats 37 a and 37 b, respectively.

On the other hand, for the six rotating side electrodes 40 a to 40 f, asalso shown in FIG. 7, the one pair of axially adjacent rotating sideelectrodes 40 a and 40 b are stacked with a ring-shaped rotating sideinsulating seat 41 a interposed therebetween, the second pair of axiallyadjacent rotating side electrodes 40 c and 40 d are stacked with aring-shaped rotating side insulating seat 41 b interposed therebetween,and the third pair of axially adjacent rotating side electrodes 40 e and40 f are stacked with a ring-shaped rotating side insulating seat 41 cinterposed therebetween. The one pair of electrodes 40 a and 40 b, thesecond pair of electrodes 40 c and 40 d, and the third pair ofelectrodes 40 e and 40 f form three individual rotating side electrodestacks 42 a to 42 c with the rotating side insulating seats 41 a to 41c, respectively.

A group of the two stationary side electrode stacks 38 a and 38 b andanother group of the three rotating side electrode stacks 42 a to 42 care arranged between the stationary side electrodes 36 a and 36 f as apair of end electrodes located at axial ends of the electric signal slipring 31 so that one from one group and one from the other alternateaxially or vertically and all in each group are axially aligned.

Furthermore, between each of the stationary side electrodes 36 a and 36f as the end electrodes and an axially faced one of the rotating sideelectrodes 40 a and 40 f of the rotating side electrode stacks 42 a and42 c, and between each faced two of the stationary and rotating sideelectrodes 36 b to 36 e and 40 b to 40 e of the axially adjacentstationary and rotating side electrode stacks 38 a, 38 b and 42 a to 42c, spherical bodies 44 of steel balls are interposed which serve asrolling elements for rolling on each faced two of these electrodes 36 ato 36 f and 40 a to 40 f through rotation of the rotor 6 relative to thestator 1 to pass electric signals between the faced two of theelectrodes 36 a to 36 f and 40 a to 40 f. As shown in FIG. 4, theplurality of spherical bodies 44 are disposed circumferentially atregular intervals between each faced two of the electrodes 36 a to 36 fand 40 a to 40 f. Each of the spherical bodies 44, 44, . . . is receivedand held in a corresponding one of retaining holes 45 a in aring-plate-shaped retainer 45 located between each faced two of theelectrodes 36 a to 36 f and 40 a to 40 f. Each spherical body 44 isformed of, for example, a steel ball obtained by quenching carbon steel,and its surface is plated with silver, for example. Plating materialsused for plating the spherical body 44 are desirably good conductivematerials having the effect of rust prevention of the electrodes 36 a to36 f and 40 a to 40 f themselves.

The lower flange 32 b of the inner housing 32 is formed at the topsurface with an annular spring groove 47, and the spring groove 47accommodates a spring 48 as a pressing means for pressing the stationaryside electrode 36 f as the lower end electrode toward the stationaryside electrode 36 a as the upper end electrode. A ring-plate-shapedinsulator 49 is interposed between the stationary side electrode 36 f asthe lower end electrode and the spring 48 so that the spring 48 pressesthe electrode 36 f through the insulator 49.

The upper flange 32 a of the inner housing 32 is formed at the outerperiphery with an annular packing groove 50, and the packing groove 50accommodates a rubber-made packing 51 of substantially V-shaped sectionhaving a lip 51 a with the lip 51 a pressing against the top surface ofthe outer housing 33. The packing 51 provides a seal between the upperends of both the housings 32 and 33.

A portion of the inner housing 32 located toward the stator 1 is formedwith a rectangular, bottomed hole 53 opening into the top surface of theinner housing 32. The outer periphery of the cover 4 of the stator 1 ismounted integrally with a connector fitting part 55 having a threadedhole 54, and a stationary side connector 56 is secured to the threadedhole 54 by screw-threaded engagement. The threaded hole 54 of theconnector fitting part 55 is communicated with the bottomed hole 53 ofthe inner housing 32 via a through hole 57 formed in the cover 4.Furthermore, as also shown in FIG. 6, the inner peripheries of thestationary side electrodes 36 a to 36 f are provided with connectionterminals 36 g to extend to lie within the bottomed hole 53 of the innerhousing 32, respectively. The connection terminals 36 g are securelyconnected with one ends of stationary side electric wires 58,respectively. These six stationary side electric wires 58, 58, . . . runthrough the bottomed hole 53, the through hole 57 of the cover 4 and thethreaded hole 54 of the connector fitting part 55, and are thenconnected at their other ends with the stationary side connector 56.

On the other hand, a portion of the outer housing 33 located toward therotor 6 is formed at the outer periphery with a cutaway 63 formed bycutting away part of the outer housing 33 in a rectangular shape fromthe bottom surface. The outer periphery of the lower flange 9 of therotor 6 is mounted integrally with a connector fitting part 65 having athreaded hole 64, and a rotating side connector 66 is secured to thethreaded hole 64 by screw-threaded engagement. The threaded hole 64 iscommunicated with the cutaway 63 of the outer housing 33 via a throughhole 67 formed in the lower flange 9. Furthermore, as also shown in FIG.7, the outer peripheries of the rotating side electrodes 40 a to 40 fare provided with connection terminals 40 g to extend to lie within thecutaway 63 of the outer housing 33, respectively. The connectionterminals 40 g are securely connected with one ends of rotating sideelectric wires 68, respectively. These six rotating side electric wires68, 68, . . . run through the cutaway 63, the through hole 67 of thelower flange 9 and the threaded hole 64 of the connector fitting part65, and are then connected at their other ends with the rotating sideconnector 66.

By conducting electricity between the individual stationary sideelectrodes 36 a to 36 f and the faced individual rotating sideelectrodes 40 a to 40 f via the spherical bodies 44, six kinds ofelectric signals are passed even between the stator 1 and the rotor 6both relatively rotated, as shown in Table 1.

TABLE 1 Stator side Spheric Rotor side Signal (Inner housing) body(Outer housing) 1 Stationary side electrode 36a 44 Rotating sideelectrode 40a Rotating side insulating seat 41a 2 Rotating sideelectrode 40b 44 Stationary side electrode 36b Stationary sideinsulating seat 37a 3 Stationary side electrode 36c 44 Rotating sideelectrode 40c Rotating side insulating seat 41b 4 Rotating sideelectrode 40d 44 Stationary side electrode 36d Stationary sideinsulating seat 37b 5 Stationary side electrode 36e 44 Rotating sideelectrode 40e Rotating side insulating seat 41c 6 Rotating sideelectrode 40f 44 Stationary side electrode 36f

Furthermore, as shown in FIGS. 2, 3 and 6, the outer periphery of eachof the stationary side electrodes 36 a to 36 f has a circular shape,while the inner periphery thereof is provided with a plurality of (fivein the example shown) abutments 36 h, 36 h, . . . extending inwardly atpositions circumferentially equally spaced from each other. Thestationary side electrodes 36 a to 36 f are fitted and borne against theouter periphery of the inner housing 32 with the abutments 36 h, 36 h, .. . registering against it. A certain clearance is left between theouter peripheries of the stationary side electrodes 36 a to 36 f and theinner periphery of the outer housing 33.

On the other hand, as shown in FIGS. 2, 3 and 7, the inner periphery ofeach of the rotating side electrodes 40 a to 40 f has a circular shape,while the outer periphery thereof is provided with a plurality of (fivein the example shown) abutments 40 h, 40 h, . . . extending outwardly atpositions spaced circumferentially equally from each other. The rotatingside electrodes 40 a to 40 f are fitted and borne against the innerperiphery of the outer housing 33 with the abutments 40 h, 40 h, . . .registering against it. A certain clearance is left between the innerperipheries of the rotating side electrodes 40 a to 40 f and the outerperiphery of the inner housing 32.

Furthermore, as shown in FIG. 1, the side surface of the connectorfitting part 55 which is mounted on the outer periphery of the outwardflange 2 of the stator 1 is formed with an air blowing hole 59communicating with the threaded hole 54 inside thereof. The side surfaceof the connector fitting part 65 which is mounted on the outer peripheryof the lower flange 9 of the rotor 6 is formed with an air blowing hole69 communicating with the threaded hole 64 inside thereof. The airblowing hole 59 in the side surface of the connector fitting part 55toward the stator 1, the threaded hole 54 inside thereof, the throughhole 57 of the cover 4, the bottomed hole 53 of the inner housing 32 andthe cutaway 63 of the outer housing 33 of the electric signal slip ring31, the through hole 67 of the lower flange 9 of the rotor 6, thethreaded hole 64 of the connector fitting part 65, and the air blowinghole 69 in the side surface thereof form an air blowing passage 61 oneend of which opens into the stator 1 at the air blowing hole 59 in theconnector fitting part 55 and the other end of which opens into therotor 6 at the air blowing hole 69 in the connector fitting part 65. Theintermediate zones of the air blowing passage 61 are in communicationthrough the ways among the stationary side electrodes 36 a to 36 f andthe rotating side electrodes 40 a to 40 f in the electric signal slipring 31. For this purpose, the air blowing passage 61 is constituted byincluding the electric wire insertion holes for inserting therein theelectric wires 58 and 68 connecting to the electric signal slip ring 31.

In this way, as shown in FIGS. 9 and 10, when compressed air is blown inthrough the air blowing hole 59 in the side surface of the connectorfitting part 55 toward the stator 1 while the stator 1 and the rotor 6are relatively rotated, the air is supplied to the bottomed hole 53 ofthe inner housing 32 of the electric signal slip ring 31 and split fromthe bottomed hole 53 into both circumferential sides, and these twosplit air flows are merged into a single flow at the cutaway 63 of theouter housing 33 and then blown out through the air blowing hole 69 inthe side surface of the connector fitting part 65 of the rotator 6. Onthe contrary, when compressed air is blown in through the air blowinghole 69 in the side surface of the connector fitting part 65 toward therotor 6, the air is run through the air blowing hole 61 in the reversedirection and blows out through the air blowing hole 59 in the sidesurface of the connector fitting part 55 toward the stator 1.

Therefore, according to this embodiment, when the rotor 6 is rotatingrelative to the stator 1 during operation of the welding robot forwelding work with the welding gun, water and air are passed between thestator 1 and the rotor 6 through the two water passages 12 and 13 andthe air passage 14 in the swivel joint 11. Furthermore, in the powerslip ring 21, the slide contacts 26, 26, . . . on the stator 1 sidecomes into sliding contact with the collector rings 22, 22, . . . on therotor 6 side, respectively, so that welding power at a large current issupplied from the stator 1 side to the rotor 6 side.

Furthermore, through the electric signal slip ring 31, six kinds ofelectric signals are passed between the stator 1 and the rotor 6. Inthis connection, in the electric signal slip ring 31, two stationaryside electrode stacks 38 a and 38 b are formed individually by each pairof two of the four stationary side electrodes 36 b to 36 e excluding theend electrodes from the six stationary side electrodes 36 a to 36 f andone of the stationary side insulating seats 37 a and 37 b, and threerotating side electrode stacks 42 a to 42 c are formed individually byeach pair of two of the six rotating side electrodes 40 a to 40 f andone of the rotating side insulating seats 41 a to 41 c. The electrodestacks 38 a and 38 b and the electrode stacks 42 a to 42 c arealternately arranged between the stationary side electrodes 36 a and 36f which are the end electrodes. Between each of the stationary sideelectrodes 36 a and 36 f as the end electrodes and a corresponding oneof the rotating side electrodes 40 a and 40 f of the rotating sideelectrode stacks 38 a and 38 b, and between each faced two of thestationary and rotating side electrodes 36 b to 36 e and 40 b to 40 e ofthe axially adjacent stationary and rotating side electrode stacks 38 a,38 b and 42 a to 42 c, the plurality of spherical bodies 44, 44, . . .are interposed. Thus, the spherical bodies 44, 44, . . . lie betweeneach of the stationary side electrodes 36 a to 36 f and a correspondingone of the rotating side electrodes 40 a to 40 f for transmitting orreceiving signals from or to each said stationary side electrode, andthe stationary side electrodes 36 a to 36 f and the rotating sideelectrodes 40 a to 40 f relatively move while rolling the sphericalbodies 44, 44, . . . . In this way, the rotary joint has a structure inwhich six different electric signals are passed between the stator 1 andthe rotor 6, and at the same time suppresses the occurrence of slip onthe electrodes as much as possible. This provides stable transmissionand reception of an electric signal between each of the stationary sideelectrodes 36 a to 36 f and the corresponding one of the rotating sideelectrodes 40 a to 40 f.

Furthermore, the stationary side electrode 36 f as the lower endelectrode is pressed toward the stationary side electrode 36 a as theupper end electrode by the spring 48 so that the stationary sideelectrodes 36 b to 36 e and the rotating side electrodes 40 a to 40 fare sandwiched between the end electrodes (stationary side electrodes 36a and 36 f) to press them against the spherical bodies 44, 44, . . . .Therefore, the occurrence of slip between each of the stationary sideelectrodes 36 a to 36 f and the corresponding one of the rotating sideelectrodes 40 a to 40 f can be suppressed with higher certainty, therebyproviding more stable transmission reception of an electric signalbetween each of the electrodes 36 a to 36 f and the corresponding one ofthe electrodes 40 a to 40 f.

Furthermore, the surfaces of the spherical bodies 44, 44, . . . and theelectrodes 36 a to 36 f and 40 a to 40 f are plated with silver or othermaterials. Therefore, the contact resistance between each spherical body44 and the adjacent electrodes 36 a to 36 f and 40 a to 40 f can beconstantly held at a small value.

Moreover, the stationary side electrodes 36 a to 36 f are fitted andborne against the outer periphery of the inner housing 32 with theabutments 36 h, 36 h, . . . registering against it, and a certainclearance is left between the outer peripheries of the stationary sideelectrodes 36 a to 36 f and the inner periphery of the outer housing 33.On the other hand, the rotating side electrodes 40 a to 40 f are fittedand borne against the inner periphery of the outer housing 33 with theabutments 40 h, 40 h, . . . registering against it, and a certainclearance is left between the inner peripheries of the rotating sideelectrodes 40 a to 40 f and the outer periphery of the inner housing 32.Thus, even if the alignment of the axis of the outer housing 33 of theelectric signal slip ring 31 with the axis of the inner housing 32thereof, as shown in FIG. 8A, is disturbed during rotation of the rotor6, for example, even if the axis of the outer housing 33 on the rotor 6side is displaced, as shown in FIG. 8B, in one direction (leftwards inthe figure) relative to the axis of the inner housing 32 on the stator 1side, the inner peripheries of the rotating side electrodes 40 a to 40 ffitted on the inner periphery of the outer housing 33 only abut againstthe outer periphery of the inner housing 32 to eliminate the clearancetherebetween. On the contrary, even if the axis of the outer housing 33is displaced, as shown in FIG. 8C, in the other direction (rightwards inthe figure) relative to the axis of the inner housing 32, the outerperipheries of the stationary side electrodes 36 a to 36 f fitted on theouter periphery of the inner housing 32 only abut against the innerperiphery of the outer housing 33 to eliminate the clearancetherebetween. Therefore, even if a misalignment between the axes of thestator 1 and the rotor 6 occurs, each spherical body 44 can be rolledstably between each faced two of the electrodes 36 a to 36 f and theelectrodes 40 a to 40 f to ensure transmission of an electric signaltherebetween.

In addition, since the raceways for spherical bodies 44 of theelectrodes 36 a to 36 f and 40 a to 40 f are formed in flat surfaces,the plurality of spherical bodies 44, 44, . . . can be rolled withhigher stability between each faced two of the electrodes 36 a to 36 fand the electrodes 40 a to 40 f. Therefore, even if a misalignmentbetween the axes of the stator 1 and the rotor 6 occurs, it can beensured that an electric signal is transmitted with higher stability.

Furthermore, the air blowing passage 61 is formed by the air blowinghole 59 in the side surface of the connector fitting part 55 toward thestator 1, the threaded hole 54 inside thereof, the through hole 57 ofthe cover 4, the bottomed hole 53 of the inner housing 32 and thecutaway 63 of the outer housing 33 of the electric signal slip ring 31,the through hole 67 of the lower flange 9 of the rotor 6, the threadedhole 64 of the connector fitting part 65, and the air blowing hole 69 inthe side surface thereof. Therefore, as shown in FIGS. 9 and 10, therecan be periodically carried out the operation of blowing compressed airinto, for example, the air blowing hole 59 in the side surface of theconnector fitting part 55 toward the stator 1 while relatively rotatingthe stator 1 and the rotor 6 (preferably, two turns or more), supplyingthe air into the bottomed hole 53 of the inner housing 32 of theelectric signal slip ring 31 to split it from the bottomed hole 53 intoboth circumferential sides, merging both the air flows into a singleflow at the cutaway 63 of the outer housing 33, and then blowing out theair flow through the air blowing hole 69 in the side surface of theconnector fitting part 65 of the rotator 6, and subsequently theoperation of blowing compressed air, in reverse, into the air blowinghole 69 in the side surface of the connector fitting part 65 of therotator 6 while likewise relatively rotating the stator 1 and the rotor6, running the air through the air blowing hole 61 in the reversedirection, and then blowing out the air through the air blowing hole 59in the side surface of the connector fitting part 55 toward the stator 1(these operations may be carried out in the reverse order). Thus, evenif wear particles are produced on the electric signal slip ring 31because of wear of the electrodes 36 a to 36 f and 40 a to 40 f, the airflow through the air blowing passage 61 can blow off the wear particlestogether with the blown air to the outside of the housings 32 and 33(rotary joint A). Therefore, wear particles can be removed with ease,thereby providing stable transmission of electric signals between eachfaced two of the electrodes 36 a to 36 f and 40 a to 40 f for a longperiod of time.

Also, in this case, the air blowing passage 61 is constituted byincluding the electric wire insertion holes for inserting therein theelectric wires 58 and 68 connecting to the electric signal slip ring 31.Thus, air can be blown on the electric signal slip ring 31 using theexisting electric wire insertion holes, and therefore the structure ofthe air blowing passage 61 can be simplified. Alternatively, the airblowing passage 61 may be provided separately without using the existingelectric wire insertion holes. However, the combination of the airblowing passage with the electric wire insertion holes as describedabove is desirable because its structure can be simplified.

INDUSTRIAL APPLICABILITY

According to the present invention, in a rotary joint including anelectric signal slip ring for passing different electric signals betweena stator and a rotor, a stationary side electrode stack is provided onthe stator side by interposing a ring-shaped stationary side insulatinglayer between each pair of axially adjacent ring-plate-shaped stationaryside electrodes, while a rotating side electrode stack is provided onthe rotor side by interposing a ring-shaped rotating side insulatinglayer between each pair of axially adjacent ring-plate-shaped rotatingside electrodes. The stationary side electrode stack and the rotatingside electrode stack are axially alternately arranged between a pair ofend electrodes located at both axial ends of the electric signal slipring, and a plurality of rolling elements are disposed between theaxially faced two of the electrodes, thereby passing electric signalsbetween the faced electrodes. Therefore, the present invention has ahigh industrial applicability in that the occurrence of slip on theelectrodes is suppressed as much as possible through the rolling ofrolling elements between the faced electrodes, thereby providing stabletransmission and reception of an electric signal between the facedstationary and rotating side electrodes and in turn improving thereliability of the rotary joint.

1. A rotary joint including a stator and a rotor rotatably coupled andsupported to the stator, an annular space being formed between thestator and the rotor, and an electric signal slip ring provided in theannular space for passing electric signals between the stator and therotor, the rotary joint characterized in that an air blowing passage isprovided which has one end opening into the stator at a first airblowing hole, the other end opening into the rotor at a second airblowing hole, and an intermediate part passing through the annular spacein which the electric signal slip ring is provided, and the rotary jointis configured to alternately carry out a first air blowing operation anda second air blowing operation to discharge wear particles produced bythe electric signal slip ring to the exterior of the rotary joint,wherein in the first air blowing operation, air is blown into the airblowing passage through one of the first and second air blowing holeswhile relatively rotating the stator and the rotor, and the air isdischarged through the other of the first and second air blowing holes,and wherein in the second air blowing operation, air is blown into theair blowing passage through the other of the first and second airblowing holes while relatively rotating the stator and the rotor, andthe air is discharged through said one of the first and second airblowing holes so that direction of air blowing through the air blowingpassage is reversed from the first air blowing operation.
 2. A rotaryjoint including a stator, a rotor rotatably coupled and supported to thestator, and an electric slip ring for passing electric signals betweenthe stator and the rotor, characterized in that an air blowing passageis provided which has one end opening into the stator at an air blowinghole, the other end opening into the rotor at an air blowing hole and anintermediate part passing through the electric signal slip ring, the airblowing passage including an electric wire insertion hole for insertingtherein an electric wire connecting to the electric signal slip ring,and the rotary joint is configured so that an air blowing operation ofblowing air into the air blowing passage through one of the air blowinghole on the stator side and the air blowing hole on the rotor side whilerelatively rotating the stator and the rotor and discharging the airthrough the other air blowing hole and another air blowing operation ofblowing air into the air blowing passage through the other air blowinghole while relatively rotating the stator and the rotor and dischargingthrough said one air blowing hole is alternately carried out.